R. T. Major (Science 157, 1967, 1270-1273) was the first person to report on the isolation of a lactone having the formula C.sub.15 H.sub.18 O.sub.8 from the leaves of the Ginkgo biloba tree. K. Weinges and W. Bahr termed the substance "bilobalide" and investigated and described the physicochemical properties of bilobalide and its derivatives (Liebigs Ann. Chem., 724, 1969, 214-216). According to a joint publication by the research teams of K. Nakanishi et al., R. T. Major et al., and K. Weinges et al. (J. Amer. Chem. Soc. 93, 1971, 3544-3546), bilobalide has the formula I ##STR1## Since 1965 extracts from leaves of the Ginkgo biloba tree have been used in the therapy of central and peripheral circulatory disturbances. Such extracts contain flavone glyocsides as their main components and have also been standardized to include those ingredients. A typical representative of this group is 5,7,3',4'-tetrahydroxyflavono-3-O-alpha-rhamnopyranosyl-4-O-beta-D-(6'"-tr ans-cumaroyl)glycopyranoside having the formula II ##STR2## Generally, those extracts may also contain lower amounts of bilobalide and ginkgolides A, B, C, and J.
U.S. Pat. No. 4,571,407 discloses that bilobalide is useful in the treatment of various degenerative, neuronal diseases. Such diseases particularly include neuropathies, encephalopathies, and myelopathies associated with one or more of the following symptoms: paresthesias, pareses, abnormal reflexes, muscular atrophies, muscular spasms, tremors, headaches, speech disorders, hearing defects, dizziness, disturbances of consciousness, impaired coordination, etc.
Surprisingly, it has now been found that bilobalide exhibits anxiolytic activities in addition to the known pharmacological effects on degenerative, neurological diseases. This is the first time that psychopharmacological effects of bilobalide have become known.
The fear that actually represents a useful mechanism to protect the human being in that it frequently warns him against exposing himself to certain dangers becomes pathological when it is unfounded or extremely strong. Anxiety patients show, among others, symptoms such as agitation, unrest, apathy and frequently have difficulty in falling asleep and in sleeping through.
Pathological fear is a frequently occurring symptom that is often not paid enough attention to, although fear is frequently the cause of so-called psychosomatic diseases. Pathological fear has so far been treated by psychotherapy and/or drug therapy using anxiolytic drugs.
The pharmacological anxiolytics are predominantly derived from the group of benzodiazepines (e.g., diazepam). More recent anxiolytics have been characterized pharmacologically as 5HT.sub.1a agonists (e.g., buspiron). Surprisingly, bilobalide shows activity essentially corresponding to that of diazepam or buspiron in various animal models.